The present invention relates to an image forming apparatus having body, a photoconductive drum or similar image carrier for forming an electrostatic latent image thereon, a developing unit or similar processing unit supported by the apparatus body to be movable toward and away from the image carrier and having a rotary body pressed against the surface of the image carrier either directly or through other members and a support for supporting it rotatably, and a biasing arrangement means for biasing the processing unit in a direction for pressing the rotary body of the processing unit against the image carrier.
An electrophotographic copier, printer, facsimile machine or similar image forming apparatus is extensively used today. A prior art electrophotographic copier, for example, has an image carrier in the form of a photoconductive element and a developing unit or similar processing unit which is located in close proximity to the drum. Usually, the developing unit has a toner container accommodating a toner or developer therein, and a developing roller supported by the toner container with a part thereof being exposed to the outside through an opening of the container. The toner container is constantly biased by a compression spring or similar biasing arrangement to maintain the developing roller in pressing contact with the drum. The developing unit is removably mounted on a body of the copier to facilitate replacement thereof which will be needed when the unit runs out of toner, maintenance, etc. Specifically, when the developing unit is mounted or dismounted, the toner container is guided by a guide arrangement in a direction in alignment with the direction, the developing roller is urged against the drum, i.e., in the horizontal direction or in the right-and-left direction. However, the toner container is not so constructed as to be movable up and down and is, therefore, not easily to handle. It will be apparent that a toner container capable of being lifted up or lowered straight down would promote efficient mounting and dismounting of the developing unit. It has been customary to provide some play between guide members which constitute the guide arrangement in order to allow the guide arrangement to guide the toner container smoothly. This is disadvantageous, however, in that the toner container is apt to shake up and down due to the play, resulting in the quality of an image being degraded. Further, substantial frictional resistance is developed between the biasing arrangement or compression spring and the toner container to disturb the smooth movement of the toner container in the horizontal direction. On the other hand, since the toner container is constantly biased toward the drum by the compression spring, it may occur that, when the toner container is spaced apart from the drum for mounting or dismounting the developing unit, the operator can inadvertently releases the toner container to cause the container and, therefore, the developing roller to hit against the drum due to the action of the spring. This would damage the developing roller and the drum. To avoid such an occurrence, one has to maintain the toner container spaced apart from the drum by hand throughout the replacement or maintenance, resulting in inefficient manipulations.